1. Field of the Invention
This invention is related to fuels, especially hydrocarbon fuels, and lubricants, especially lubricating oils, and, more particularly, to a lubricant composition containing a class of anti-wear, anti-fatigue, and extreme pressure additives for such fuels and lubricants that are derived from hydroxy carboxylic acid esters and hydroxy polycarboxylic acid esters.
2. Description of Related Art
In developing lubricating oils, there have been many attempts to provide additives that impart anti-fatigue, anti-wear, and extreme pressure properties thereto. Zinc dihydrocarbyldithiophosphates (ZDDP) have been used in formulated oils as anti-wear additives for more than 50 years. However, zinc dihydrocarbyldithiophosphates give rise to ash, which contributes to particulate matter in automotive exhaust emissions, and regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, phosphorus, also a component of ZDDP, is suspected of limiting the service life of the catalytic converters that are used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain undiminished the anti-wear properties of the lubricating oil.
In view of the aforementioned shortcomings of the known zinc and phosphorus-containing additives, efforts have been made to provide lubricating oil additives that contain neither zinc nor phosphorus or, at least, contain them in substantially reduced amounts. Illustrative of non-zinc, i.e., ashless, non-phosphorus-containing lubricating oil additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazoles and unsaturated mono-, di-, and tri-glycerides disclosed in U.S. Pat. No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U.S. Pat. No. 5,514,189.
U.S. Pat. No. 5,512,190 discloses an additive that provides anti-wear properties to a lubricating oil. The additive is the reaction product of 2,5-dimercapto-1,3,4-thiadiazole and a mixture of unsaturated mono-, di-, and triglycerides. Also disclosed is a lubricating oil additive with anti-wear properties produced by reacting a mixture of unsaturated mono-, di-, and triglycerides with diethanolamine to provide an intermediate reaction product and reacting the intermediate reaction product with 2,5-dimercapto-1,3,4 thiadiazole.
U.S. Pat. No. 5,514,189 discloses that dialkyl dithiocarbamate-derived organic ethers have been found to be effective anti-wear/antioxidant additives for lubricants and fuels.
U.S. Pat. No. 3,293,181 discloses that zinc dialkyl dithiophosphates of improved thermal stability can be provided by the zinc salts of mixed dialkyl dithiophosphoric acids in which the alkyl groups are derived from a mixture of at least two different branched chain primary alcohols, one of the alcohols being isobutyl alcohol and the other containing at least six carbon atoms.
U.S. Pat. No. 3,396,109 discloses the preparation of phosphorus- and nitrogen-containing compositions by reacting a metal salt of a phosphinodithioic acid, especially a zinc salt of a diarylphosphinodithioic acid, with an amine, especially an aliphatic amine having from one to about forty carbon atoms. The compositions are said to be useful as additives for lubricating oils and automatic transmission fluids, in which they act as oxidation inhibitors and anti-wear agents. They are also said to afford synergistic oxidation inhibition properties when used with phenyl β-naphthyl amines.
U.S. Pat. No. 3,397,145 discloses an alkylthiophosphoric acid salt formed by the addition reaction thereof to a tertiary nitrogen atom of a condensation product containing said tertiary atom and comprising a polymeric reaction product.
U.S. Pat. No. 3,442,804 discloses a lubricating composition containing a small amount of a particularly defined zinc phosphorodithioate. The zinc phosphorodithioate is illustrated by that derived from dihydrocarbon phosphorodithioic acid in which the hydrocarbon radicals are primary alkyl radicals and consist of a mixture of lower molecular weight radicals (i.e., having less than 5 carbon atoms) and higher molecular weight radicals (i.e., having at least 5 carbon atoms). In the particularly defined zinc phosphorodithioate, the ratio of the lower molecular weight radicals to the higher molecular weight radicals, expressed on a molar basis, is with the range of 1:1 to 3:1.
U.S. Pat. No. 3,637,499 discloses lubricating oil compositions containing as anti-wear and detergent-inhibitor additives therein, an amine neutralized derivative of a dithiophosphoric acid prepared by reacting a long chain alkenyl-substituted C3-C8 monocarboxylic acid of 400-3,000 molecular weight with a primary or secondary hydrocarbylol amine, reacting the resultant amide with a phosphorus sulfide and neutralizing the resultant dithiophosphoric acid with a polyamino compound.
U.S. Pat. No. 4,151,102 discloses a synthetic bearing lubricant that prevents wear and is such that when it contaminates the rolling lubricant the rolled product is not stained. The bearing lubricant contains poly-isobutene, at least one ester of a C2 to C5 alcohol with an α-hydroxy-mono carboxylic acid or an α-hydroxy-dicarboxylic acid, and at least single or poly unsaturated C13 to C19 carboxylic acid.
U.S. Pat. No. 4,741,848 discloses a method of preparing boron-containing compositions that comprises reacting at least one hydroxy-substituted ester, amide or imide with a boron compound. Such boron-containing compositions are said to be useful in fuel compositions and in lubricating oils and to provide the lubricating oils with anti-wear and/or friction-reducing properties.
U.S. Pat. Nos. 5,084,195 and 5,300,243 disclose N-acyl-thiourethane thioureas as anti-wear additives specified for lubricants or hydraulic fluids.
U.S. Pat. No. 5,338,470 discloses alkylated citric acid derivatives obtained as a reaction product of citric acid and an alkyl alcohol or an amine that are said to be effective antiwear and friction modifying additives for fuels and lubricants.
U.S. Pat. No. 5,498,809 discloses oil soluble copolymers derived from ethylene and 1-butene which have a number average molecular weight between about 1,500 and 7,500, at least about 30 percent of all polymer chains terminated with ethylvinylidene groups, and ethylene-derived content of not greater than about 50 weight percent, and which form solutions in mineral oil free of polymer aggregates, as determined by light scattering measurements. Lubricating oil additives, particularly dispersants, produced by the functionalization and derivatization of these copolymers are said to have enhanced performance (e.g., improved dispersancy and pour point) in lubricating oil compositions, attributable in part to the combination of properties characterizing the copolymers.
CS 254033 teaches the use of 2-ethylhexyl-4-hexadecylsalicylic acid as a friction modifier in motor oils.
EP 562405 discloses the use of citrate esters for refrigeration compressor lubricants.
FR 2205931 discloses the use of butyl lactate 33% wt as part of a base stock formulation. 0.7% ZDDP is used.
JP1995268369A discloses additives consisting of hydroxy polycarboxylic ester compounds., e.g., (R1—CO2)3C—OH, where R1 is alkyl group of 1-18 carbons. The lubricating oil compounds contain 0.1-40 wt. % of the hydroxy polycarboxylic ester additives. The additives are said to provide abrasion resistance to pure lubricating oils.
JP 2000290669 discloses using an 90-100% of an ester with up to 10% of a nonionic surfactant as an agent for stripping water from fuel oils or gasoline. The preferred esters are methyl a-hydroxyisobutyrate, ethyl a-hydroxyisobutyrate, hexyl a-hydroxyisobutyrate, methyl lactate, octyl lactate, hexyl glycolate, and octyl glycolate.
WO 2001060954 discloses a-hydroxymonocarboxylic esters as diesel fuel additive, preferably at 3-6%.
Mirci, L. et al., Synthetic Lubrication (2003), 20(1) 39-52 discusses the use of complex esters based on citric acid as synthetic base stocks.
Ponomorenko, A. G. et al., Trenie I Iznos (1998), 9(2) 305-310 (CAN 109:233832) state that the anti-wear and friction properties of individual and tartaric esters are improved when they are diluted with paraffin oil. The ester should not be less than 30-50% of the mixture.
The disclosures of the foregoing references are incorporated herein by reference in their entirety.